1.He asked me another question (since ) I could answer the first one.
2.I was doing my homework (when ) suddenly a dog came in.
3.The students sang ( as) they went along.
4.( While) I was writing letters last night,he was watching TV.
5.I'll be more careful ( ) what you have said.(该题有问题）
6.Please wait here (until ) I come back.
7.It is so dark outside ( because) it is raining.
8.( Since) everyone is here,let's begin our meeting.
9.(As soon as ) I get to Beijing,I will write to you.
10.( If) it rains tomorrow,I will not go to Shanghai.